Windmill sail



FIG. 1 is a right side elevation view of a windmill sail showing our new design, the left side elevation view being a mirror image;

FIG. 2 is a first perspective view thereof;

FIG. 3 is a right side view thereof, in an alternate deployment state;

FIG. 4 is a left side view thereof, of that shown in FIG. 3;

FIG. 5 is a second perspective view thereof; and,

FIG. 6 is an enlarged plan view thereof. 

CLAIM The ornamental design for a windmill sail, as shown and described. 